The present invention relates to weaving looms and more particularly to an apparatus for selectively inserting weft yarns into the shed in a weaving loom of the type which is capable of using a plurality of weft yarns having different natures, particularly colors. The weaving loom to which the present invention appertains is, furthermore, typically of the shuttleless type utilizing a jet stream of fluid for shooting the pick of weft yarn into the weaving shed, although the the present invention is applicable to any other type of weaving looms.
A representative example of the apparatus of the above described nature uses a cam unit including at least one lobular cam having lobe portions and bottom portions alternately arranged about the axis of rotation of the cam. The cam is driven to turn about the axis thereof under the control of suitable weft selector signal supply means such as for example a pattern card arrangement storing signals representative of a predetermined schedule in accordance with which a weft yarn to be inserted into the weaving shed is selected out of the weft yarns respectively detained in a plurality of weft shooting members or nozzles. A cam follower roller is in rolling contact with the cam surface of the cam and is operatively connected to the weft shooting nozzles by a suitable link mechanism so that any of the weft shooting nozzles is moved into a position ready to shoot into the weaving shed the pick of the weft yarn which has been detained therein as the cam follower roller is raised and lowered over the axis of rotation of the cam in each cycle of operation of the loom.
When the cam is rotated about the axis thereof from an angular position receiving the cam follower roller on one of its lobe portions into an angular position receiving the cam follower roller on one of its bottom portions, the cam follower roller is lowered over the axis of rotation of the cam. As the cam is thus moved closer to the latter angular position, the cam tends to be rotated at an increasing velocity about the axis thereof and is thus liable to turn beyond the angular position receiving the cam follower roller on one of its bottom portions. When, conversely, the cam is rotated from the angular position having an cam follower roller on one of its bottom portions into an angular position having the cam follower roller received on one of its cam lobe portions, the cam tends to turn at a decreasing velocity about the axis thereof and is thus liable to fail to accurately reach the angular position receiving the cam follower roller on one of its cam lobe portions. Such tendencies are pronounced when the cam is driven at an increased velocity.